A lens array (hereinafter abbreviated as "SLA") constituted by a number of parabolic refractive index distributing rod lenses which are arrayed to make their optical axes parallel has been used widely to focus one-dimensional image information on the surface of an original document onto a contact type image sensor.
Recently, it has been preferred to use a so-called "perfect contact type image sensor" which is constituted by a contact type image sensor having light leading windows, so that an illuminating light source placed at the back side of this image sensor illuminates an original document though the light leading window, and an array of photo-detecting portions disposed close to the light leading windows detect reflected light from the original document. In such a case, the contact sensor and the original document are disposed so close without using an SLA.
More recently, an optical system of a "semi-perfect contact type" which is considered as an intermediate between an SLA and a perfect contact type has been proposed (Extended Abstracts of the 35th Spring Meeting 1988, The Japan Society of Applied Physics, No. 3, page 753, published on Mar. 28, 1988). In this optical system, an image is focused by polymer micro-lenses for every picture element of a contact sensor, by using a combination of a polymer micro-lens array and a photo-shield spacer.
On the other hand, in an LED or liquid crystal printer, an SLA has been used to transmit, onto a photosensitive drum, light information expressed by the flashing of an LED array or the switching of a liquid crystal shutter array.
However, an SLA needs at least about 15 mm as a so-called focal length between a one-dimensional image information surface and a focusing surface, so that this value is a limit to miniaturizing an apparatus using the SLA.
On the other hand, since the perfect contact type image sensor has no focusing system such as a lens or the like, there has been a problem that image information is faded on an image sensor if the distance between the image sensor and an original document becomes even slightly large. It is therefore necessary to maintain the sensor surface always in contact with an original document, so that there has been a problem that the sensor surface is apt to be damaged.
Further, a photo-shield spacer in the semi-perfect contact type optical system is formed by overlaying ten stainless steel plates of about 50 .mu.m thick in which very small holes are made by chemical etching, so producing such a photo-shield spacer is extremely troublesome.